The authors present their results concerning the possibility of using a polynuclear coordination compound, [(FeFeMn)-Fe-II-Mn-III(C2O4)(2)(OH)(3)(H2O)(3)].H2O, as a source for manganese ferrite. The polynuclear compound synthesized by a forced hydrolysis has been characterized by chemical analysis, electronic and vibrational spectra, X-ray powder diffractometry, magnetic susceptibility measurements and thermal analysis. This paper also presents a non-isothermal kinetic study of the decomposition steps. The non-isothermal kinetic parameters have been evaluated for the whole (alpha,t) curve as well as for its significant portions.